Dr Roger Bretherton, Senior Lecturer in Psychology at the University of Lincoln, spoke about the impact caring for terminally ill adult children can have on BBC Look North.

Brothers Matthew, 39, and Michael Clark, 42, face a slow and painful death after they were both struck down with the same rare illness.

The pair – who were perfectly healthy until they reached their 30s – are among just 100 adults in the country to develop leukodystrophy, which affects the brain, nervous system and the spinal cord.

Parents Anthony and Christine Clark, who had to return from their retirement home in Spain, face the agony of nursing their sons through the final stage of their lives. The family, who previously lived in a one-bedroom council flat in Cotman Road, Lincoln, have recently moved to a larger property in Hull.

Being interviewed by BBC Look North presenter Peter Levy, Dr Bretherton said: "Parents cope in different ways. Some parents would avoid it, others would dissolve into a complete mess. Given the intense pain of the emotion we are hearing they are actually coping in quite a functional, problem-focussed, day to day way which is all you can do in a situation like this."

He added: "It's like a bereavement reaction as the parents come to terms with what's happened and are beginning to face the reality of it."